Flexible shaft



March 6, 1945. J. l.. SMITH FLEXIBLE "SHAFT Filed Aug. 5, 1943 Nk, v Y

sound casings. A large number of grinding operations can be Patented Mar. 6, 1945 UNITED STATES PATENT OFFICE FLEXIBLE SHAFT 1 I `Ioseph Leigh Smith, Glen Ellyn, Ill. Application August 5, 1943, Serial No. 497,440 I 9 Claims.

This invention relates to flexible vshafts andl particularly to a freely rotatable inter-liner or core, which inter-liner and drive core may be sold as a replacement unit for flexible shaftshaving performed more rapidly and efficiently with the tool rotating at speeds up to 20,000 R. P. M. than at substantially slower speeds. Although this has long been known, such speeds have not been common because the work commonly necessitated the use-of a, flexible shaft and in use maximum speeds for these Ishafts have been much closer to 5,000

R. P. M. than 20,000 R; P. M. kWherethe higher speeds have been used, however, the yshafts have had very short life. The speed limitation, of these or alternatively, short life flexible s hafts is attributable to friction between the drive core and the inside wall of the casingwhen such shafts are bent on `fairly short, radii. Thus, in existing' shafts, bending the shaft to a one hundred and `eighty degree arc on a radius approaching the smallest that the core will take may cut the speed down from 20,000 R. P. M.to 4,000 or 5,000 R. P. M.- The shaft becomes very hot, the lubribetween and have positioned at intervals therealong bearing assemblies of various degrees of complexity. Thesev bearing assemblies complicate the lubricating problem which already is commonly a difficult one Awithflexible shafts bel cause the spiral surface of the core tends to force the lubricant out through the tool holder end of the shaft.

The objects ofy this invention are to providev a flexible shaft that does not show markedvdeceleration when bent in an are on a radius small for the particular core in-question; to thereby prolong the 1ife` ofthe shaft; to eliminate much friction under such operating conditions; to even- `ly distribute lubricant along the shaft under such conditions; and to *accomplish these ends by means of a comparatively simple structure.

I The feature that attainsthese objects consists -of a helix positioned around the drive core Yand in length coextensive with the bendable portion of the flexible shaft, which helix is free to rotate or stand still irrespective of rotation of the core. The manner in which the inter-liner or floating helix or sleeve, as it'is variously called, functions is not clear. Experiment shows that when a flexible shaft is lying substantially straight and its core is turning at high speed,vthe floating shaft rotates slowly in the direction of the turning core. The more lubricant inside the casing, the dense'rthe lubricant and the greater increased capacity of the surface of the rotating core to affect movement in the lubricant, the greater is the tendency of the floating core to remain steady, lfor the direction of winding of the floating helix is opposite to the direction of winding of the surface layer of the exible core with the result that .the sleeve tends to forcey the lubricant backwardly toward the source of power and the lubricant tends to stop the sleeve from rotating with theeore. When the flexible shaft is bent, the

floating helix picks -up speed in the direction of I rotation of the core and this speed of the helix increases with the sharpness of the curvature of the flexible shaft. y

Additionally, in connection with his improved exible shaft, applicant has provided two new features in couplings. It has been common practice heretofore to swedge to a square cross section the driving end of the core of va flexible shaft and this square end is tted into the tool holder. Applicant provides a separate stud or pintle having a key slot which he squeeze ts over the end of the core. This pintle has a definite breaking point substantially below the breaking point of the spiral core, which results in a great advantage under the following circumstances. During grinding operations at high speeds, a workman will frequently get the stone locked in the workpiece. This places a greater strain on the motor, flexible shaft and grinding tool than they will stand and something mustbreak. In existing tools, this break usually results in the unravelling of the helicallywound core. the core is ruined and in the unwinding process, it frequently tears the innerr wall of the casing to such an extent that it is no longer usable. In

When ythis occurs coupling means at the end of the core of a exible shaft. This greatly facilitates hooking up the iiexible shaft to the source of power or the tool.

These and such other objects as may hereinafter appear are attained in the two embodiments of the invention disclosed in the accompanying drawing wherein:

Figures 1, 2a and 2b are respectively a side elevation and-enlarged cross sections on the .line 2 2 of Figure 1 yof the first embodiment of the invention;

Figure 3 is a sectional view of the first embodiment taken on the line 3--3 of Figure 1;`

and

Figures 4 and 5 are a side elevation and enlarged cross section respectively ofn the second embodiment.

Continuing to refer to the drawing, more particularly to Figure 1, the numeral ID identiiiesI a core having asurface layer consisting of a helix wound clockwise when viewed from the left. This core is conventional.- The end l2 of the core I has been swedged. to a square cross section, which is likewise conventional. The other end I4 carries a coupling member H5 tightly fitted to the core. This coupling member has a cylindrical recess I8 with a plurality of slots 20 cut back from the end and has its exterior wall threaded at 22 and tapered at 24 to receive a collar 26 having threads on its inside wall and a cone compressing shoulder 28 adapted to engage the tapered end 24 of th'e couplings i5. By tightening the collar 26, the walls of the cylindrical recess I8 will grip the shank of a tool or the like. This arrangement greatly simplifies the assembling of the drive core with the source of power.

The casing of this flexible shaft consists in a fabric layer `3l) which is conventional and which carries at either end coupling members 32 and 34. The exterior metal helices 35 and 3,8 do not extend the full length of the iiexible shaft but .are merely stiiening end members adjacent the couplings to limit the bending ofvthose portions the outer surface vof the helix 4i) and the inside of the casing 30 is Asubstantially greater'. The combination of u and a might equal as much as one-sixteenth of an inch. -These clearances are not critical so far as substantial performance' of the flexible shaft is concerned. It has been found that these clearances give improved performance over a helix whose walls are spaced equidistant from the core l0 and the inside of the casing 30.

The helices used by applicant are formed of nat strip, the width beingk ve or six times the thickness. The anglel of the helix is such that the distance between each winding does not exceed the width of the winding. This is illustrated in the second embodiment shown in Figures 4 and 5. The spacing between the` windings need not be so great, however, because a very successful oating sleeve having aspacing between the windings equal tov approximately the thickness of the steel in the lioating sleeve is very commonly used. It will be Yappreciated that there must be sumcient spacing between the windings of the helical sleeve to permit the requisite bending eof the exible shaft. The abutting walls of 'any two windings of the sleeve are parallel to each other.

As for the length of the inter-liner or iioating sleeve with respect to the nexible shaft as a whole, applicant intends that the floating sleeve shalll be coextensive with that portion of the flexible shaft which is intended to be bent. Thus, referring to Figure 1, the flexible shaft is intended to be iiexed primarily between the points 42 and -44 because the outside reinforcing helices 36 and I38` are intended to limit bending of the shaftwithin their lengths. Alit would be possible to mount applicants floating helix just between the points 42 and 44 because bending of the flexibleshaft will ordinarily occur between those ytwo points. Iii-practice, however, applicant provides the entire f length` of the drive core. between the endV couplings with aiioating helix. Thus, referring tovFigure 4, the drive core carries a pintle or stem member 48`having an enlarged bearing portion 4B and a reduced end 5l! with a key sl0tf52 therein. The other end of -the core carries a-socket coupling '54 having a bearing portion 56 similar to the bearing portion 4-8. Inside the coupling lSli-is arecess `58 with .a` drive pin 6U for` engagement with some sort of stud on the end-of armotor shaft or the like. The outside diameters of the bearing portions 48 and 56 approximatethe inside diameter of the casing 30. Between the two shoulders ofthe bearingportions 48vand 5B is positioned a floating helix 62. The helix E2 is slightly shorter leaving a space between the points 64 and 6B so that the helix can-move longitudinally of the core. The helix may expand the full length of the core under the influence of the. action of oil but beingwound in the direction opposite to the winding of the surface of the core, there is a tendency for the oilto keep the fioating helix l62 fully. extended between they bearing portions 48 andV 56 duringoperation and for the iioating helix 62 to assist in pulling the oil back from the tool end toward the drive end.

The embodiment shown in Figures 4 and 5 `ldiiers from the embodimentV shown in Figures which hasan opening 1li of approximately thev inside diameter of the casing. The bearingmember 46 rides in the opening 'I8 and assists in centering the core with respect to the casing at that point.

The advantage of applicants pintle over the swedged end I2 of the conventional core shown' in Figure 1 resides inthe fact that on an abrupt stop of the tool'caused by jamming the tool in the workpiece, the pintle will make a clean break whereas under similar circumstances, the core end l2 will commence to unravel the core. A flexible shaftv core is. ordinarily formed of a series of layers of reversely spiraled helices, each layer tightly wound on the layerV beneath it.

Once these layers have commenced to unravel, they become useless in a given length of flexible shaft and in loosening frequently tear up the inside wall ofthe casing.

In the embodiment shown in Figure 4, the floating sleeve or helix 62 is free to move longitudinally of the core 3U between the point 12 which is the shoulder `on the bearing 56 and the point 66 which is the shoulder on the bearing 48 by the distance between the point lill and the point 66. This should be contrasted with the construction shown in the first embodiment of the invention, where, referring to Figures 2a and 2b, the helix is shown to be a continuation of the collar 16 which collar tends to hold the floating helix di! from moving lengthwise of the core ID. The left-hand end `of the floating sleeve 4 is rigidly fastened to the collar 1'6.

Having thus described my invention, what I claim as new and desire to claim by United States Letters Patent is:

l. A flexible shaft comprising a casing, a drive core within said casing, and around said drive core, a floating sleeve having a length substantially coextensive with the bendable portion of said drive core, the outer and inner surfaces of said sleeve being substantially in cylindrical sur faces when the core is straight and spaced from the casingfand drive core respectively so as to permit free ro-tation of the sleeve with respect to either the casing or the core, whereby when the exible shaft is bent during rotation friction between the casing; sleeve and core is distributed among a large number of constantly changing points of contact. l

2. A flexible 'shaft comprising a casing, a drive core within said casing, and around said drive core a oating helix having `a length Substantially coextensive with the bendable portion of 'to either the casing or the core whereby when the flexible shaft is bent during rotation friction between the casing, helix -and core is distributed among a large number of constantly changing points vof contact.

3. A flexible shaft comprising a casing, a drive core within said casing, around said drive core a floating helix having a length substantially coextensive with the bendable portion of the ilexible shaft, the outer and inner surfaces of said helix being substantially in cylindrical surfaces when the core is straight and the windings being spaced from each other so as not to interfere with free bending of the flexible shaft, whereby when the iiexible shaft is bent duringrotation friction between the casing, helix and core is distributed among a large number 0f constantly changing points of contact.

4. A flexible shaft comprising a casing, a drive core having a spirally wound helix as its surface layer positioned within said casing, and a iioat-V ing helix around said drive core, said floating helix having its windings reversely spiraled to the windings of the core helix and bein-g charstantially coextensive with the length of the bendl tion of the exible shaft, the outer and inner acterized by free rotability with respect to either the core 0r the casingv and being of a length subable portion of the iiexible shaft.

5. A exible shaft comprising a casing, va drive core within said casing, and a flat strip -of material spirally wound around said core so that the spacing between each winding thereof is less than the widthof the material of the strip, said spirallywound strip having a length substantially coextensive with the length "of the bendable por surfaces of said spirally wound flat strip being substantially in cylindrical surfaces when the flex. I ible shaft is straight and spaced from the casing and drive core respectively so as to permit free rotation thereof with respect to either the casing or the core.

6. A flexible shaft comprising a casing, a coupling member positioned at Vone end of the casing, an axial opening equal to the inside diameter of the casing in said coupling, a drive core having a diameter somewhat less than the inside diameter of the casing and positioned therein and through the coupling opening, a spirally wound iioating helix around said core substantially lling the annular space between the core and the inside of the casing, and a collar seated in the outer opening of the coupling and fastened to the spirally wound. sleeve whereby the floating helix will remain in substantially fixed longitudinal position with respect to the flexible A Shaft.

7. A flexible shaft comprising a casing, a drive core within said casing, a freely rotatable helix around said drive core and substantiallyoccupy-l end of the drive core, said pintle having a bear-K' ing portion adapted to Aflt intorthe opening in i the coupling, lwhereby the corev can be inserted or withdrawn from the casing from the drive end.

8. As a replacementl part for a `flexible shaft having a casing and end coupling members, a

flexible driving core having therearound a helix,y said helix having its outer and inner surfaces A substantially in cylindrical surfaces and having a length substantially coextensive with that oi'v the driving core and freely rotatable with respect to the core.

9. As a'replacement part for a flexible Ashaft having a casing and end coupling members, a exible driving core having a collary at each end and a freely rotatable helix therearound, ysaid helix having its outer and inner surfaces sub,v stantially in cylindrical surfaces and having a f length substantially coextensive with that ofthe driving core and freely rotatable with respect to the core.

JOSEPH LEIGI-I SMITH. 

